During the examination of various media (fluids) such as gases or aqueous solutions in the past, samples had to be taken and transported to a laboratory so that the analysis of the content of the samples could be carried out there. The sample taken had to be transported to the extent possible without change to its composition. The results of the analysis were only available at a later point in time. Furthermore, the analysis of liquid media in the laboratory has the disadvantage that a continuous monitoring of measuring magnitudes on site is not possible. Therefore, the present invention relates to such photometers and measuring sounds that are used especially for measuring on site in the medium itself. These measurements are also designated on-site measurements.
Various such photometers are known in the prior art that makes use of optical systems for the analysis of the liquid medium. As a rule, such traditional photometers have a transmitter and a receiver that produce a measuring beam over a measuring stretch so that the absorption of light in the medium can be measured. The measuring beam transmitter and the measuring beam receiver are received in a closed housing and provided with transparent windows in order that the measuring beam can be guided into the medium to be examined. The previously used systems of such photometers based on optical measuring differ on the one hand in the wavelength range of the measuring beam used. For example, DE 38 39 561 C1 discloses a photometer measuring apparatus with a liquid-tightly encapsulated immersion sound that transmits a measuring beam through opposing windows out of the housing through the medium using UV light. This known photometer uses two different measuring wavelengths, whereby an apparatus for breaking down the UV light into, on the one hand, a measured value wavelength and, on the other hand, a reference value wavelength is provided. The proportion of particles of the substance to be examined in the liquid can be determined from a comparison of the two wavelengths, on the one hand, of the measured value and, on the other hand, of the reference. Here, for example, a grid is used as the means for breaking down the single measuring beam of UV light into, on the one hand, the measured value wavelength and, on the other hand, the reference value wavelength, so that the UV light beam is spectrally divided. The detection of the two wavelengths then takes place by separate detectors.
Other photometers known in the prior art use a division of the measuring beam into two different beam paths for the measuring of photometric magnitudes. This takes place in DE 33 24 606 A by filters. In DE 44 07 332 C2 the splitting of the beam paths is carried out by fiber-optical light guides. In the known device from AT 408 488 B a measuring beam produced by a light source is again specially bundled by an optical lens so that the beam can be divided, on the one hand, into a measuring beam and, on the other hand, into a reference beam. The measuring beam is conducted through windows into a measuring slot in which the medium to be examined is located. The reference beam is conducted in the interior of the housing of the photometer. The detection of, on the one hand, the measuring beam and of, on the other hand, the reference beam is realized here by a beam selector in the form of a rotating disk with perforations, so that the intensities of the reference beam and the measuring beam can be detected at different points in time. An evaluation based on a comparison between the reference beam and the measuring beam also takes place here.
Referencing of the measurement, for example, by a separately running reference beam is necessary in such photometers in order to compensate a change of the optical devices due to the aging of components. If such photometers are used on site in a liquid for a rather long time period, it can occur that the measuring parameters change based on aging phenomena. Therefore, the measuring beam emitted by the measuring beam transmitter is conducted from time to time over a reference path in which a known and stable absorption prevails. Such photometers or spectrometers are checked with reference elements that are held in the measuring beam instead of measuring samples. This is not possible in the on-site photometers concerned in the present invention. For this reason the above-described systems were developed that either operate with different wavelengths or with splitting of the beam path of the measuring beam and with usage of different detectors for the split beam.
The present invention has the task of making a photometer for on-site measurements available that allows measurements over a larger wavelength range with the simplest means possible and that also allows long-term measurements in particular in liquid media on account of the quality of its reference.
This task is solved with a photometer with the features described below, having various advantageous embodiments.